When Ross Hay struggled to put his suit trousers on four years ago and found that his BMI was classed as "obese", he decided he wanted to make a change.

The 43-year-old father-of-three launched a indefatigable fitness mission which has seen him shed four stone and run a series of arduous 100-mile ultra marathons across the UK.

Ross, from Brighton, admitted he used to be "the fat kid" in school, pleading with his mum to write a note so he could sit out PE lessons.

The Argus: Ross HayRoss Hay

He carried this aversion to exercise into his adult life, putting on weight through "going out a lot, drinking too much, eating junk and not doing any sport".

At his heaviest, Ross reached 16st 6lb, giving him a Body Mass Index (BMI) of 31. A BMI of 30 or more is categorised as "obese".

The turning point came just before Christmas in 2015 when he was struggling to fasten his suit trousers.

"I’d recently been to the doctor because I’d been having heart palpitations, so I decided to lose the weight and it all started from there," he said.

The Argus: Ross HayRoss Hay

"I used an app and lost four stone in four months, and managed to get down to a normal BMI."

But, restricted to eating a meagre 1,200 calories each day, Ross realised he still was not living a lifestyle he truly enjoyed.

"The only way I could eat more was to start doing some exercise, so I reluctantly started running," he said.

To motivate himself, Ross signed up for a gruelling 21km race in the Swiss Alps. His fitness had improved drastically as he prepared for the event, and he was able to complete the run in about four hours.

The Argus: Ross Hay after his first 100-mile raceRoss Hay after his first 100-mile race

But, as he ran, the biggest change was arguably in his mindset. Ross had caught the running bug.

He has now completed four 100-mile races in the UK including the brutal Arc of Attrition in Cornwall, which takes place in the depths of winter.

Ross, who works in finance and now lives in Switzerland, said: "The harder the race is, the better, but I still have nightmares about the South West Coast path on the Arc.

"I phoned up my wife in the middle of the night crying, saying, ‘I don’t want to do this anymore’.

"She told me that was fine but phoned back minutes later saying, ‘No, you’re bl***y well not stopping’.

The Argus: Ross Hay during the Arc of AttritionRoss Hay during the Arc of Attrition

"That was easily my worst moment. You’re on your own, in the middle of the night, on a narrow, slippery path, climbing over big rocks with the sea just down the cliffs.

"It’s the scariest thing I’ve ever done."

Ross endured a frustrating 2020 season as events were cancelled left, right and centre as a result of the coronavirus crisis.

But he has already set his sights on his next mammoth undertaking - Run Britannia, a race which takes runners all the way from Land’s End to John O’Groats.

The Argus: Ross Hay has well and truly caught the running bugRoss Hay has well and truly caught the running bug

The trek, organised by Rat Race Adventure Sports, will take place in 2023, lasting five weeks and covering a staggering 1,000-mile route that will include some of the most famous footpaths in the UK, including Offa’s Dyke in Wales and the Great Highland Way in Scotland.

Ross, who now weighs 12st 10lbs and has a BMI of 22.8, said: "I saw Run Britannia come up and I thought, ‘Man, that just sounds like the coolest lifetime achievement’.

"It’s not been done before on this route and it’s the iconic Land’s End to John O’Groats mission.

The Argus: Ross Hay has taken on a series of gruelling challenges over the last four yearsRoss Hay has taken on a series of gruelling challenges over the last four years

"I didn’t think I’d be able to get the time off work but it nagged away at the back of my mind. In the end I had a chat with my boss and he agreed to it. I can’t wait."

But, he does admit, it's a gruelling prospect. So, Ross has written a list of reasons to go through with his race plans, which he reads whenever doubt creeps into his mind.

"The last one is ‘phone my wife’,” he said, perhaps remembering the tough love that worked so well during the Arc of Attrition race . "It forces you to get those negative thoughts out of your head."